Promoção do crescimento vegetal de mudas de alface por bactérias diazotróficas produtoras de ácido indol acético

Abstract

Rhizobacteria possess characteristics related to their ability to promote the development and growth of plants through the synthesis of plant hormones. As a result, they can form associations with various plant species, thereby enhancing agricultural production in both major crops and vegetables. The objective of this study was to assess the potential of bacterial isolates in promoting the growth of lettuce seedlings. For the analyses, three bacterial isolates—MS32, MS43, and MS54—were employed, selected based on their in vitro production of indole acetic acid (IAA) in the presence of tryptophan. Additionally, two strains of Azospirillum brasilense (Ab-v5 and BR11001) were used. Isolated colonies were used to prepare bacterial suspensions in liquid Dygs medium. The concentration of bacterial inocula was adjusted using the McFarland scale, corresponding to a concentration of 15 x 10^8 CFU/mL. Lettuce seeds of the Itapuã Super cultivar were immersed in the different bacterial inoculums' suspension for 1 hour. For the control treatment, lettuce seeds were immersed in sterile liquid Dygs medium for the same duration. Subsequently, the seeds were removed and planted in plastic trays containing 200 cells, filled with commercial substrate. The trays were suspended on a bench and placed in the greenhouse for 18 days. The experiment was conducted in a completely randomized design (CRD) with six inoculation treatments (MS32, MS43, MS54, Ab-v5, BR11001, and control) and five replications. Parameters assessed included the height of the aerial part, length of the root system, diameter of the stem, weight of the aerial part, and weight of the roots. Analysis of variance (ANOVA) was performed at a 5% probability level using the F-test. For significant variables, means were compared using the Tukey-Kramer test at a 5% probability level. The inoculation of diazotrophic bacteria producing indole acetic acid resulted in significant differences in the development of lettuce seedlings. The only variable that did not exhibit a significant difference was the shoot length. Bacterial isolates MS32 and MS43 led to a 19.73% and 26.01% increase, respectively, in the biomass accumulation of lettuce plants.